Banknote acceptors are well known for use in vending and gambling machines. In a typical banknote acceptor, the banknote is inserted through an inlet slot and is driven along a path past a transversely extending array of sensors that sense characteristics of one or more faces of the banknote. It is known to use optical sensors arranged in an array to detect successive rows of data samples from the face of the banknote as it passes the array. The sensing arrangement may operate in a transmissive mode in which an optical light source is disposed to transmit light through the banknote to the sensors of the array. Alternatively, light from the source may be reflected from the face of the banknote to the optical sensors.
The data derived from the sensors may be digitised and compared with reference data corresponding to acceptable banknotes. The detection may be carried out in more than one wavelength band.
In order to allow the data from the sensor array to be compared with the reference data, the banknote needs to pass the detector array along a pre-set path. In the past, a guide rail has been provided extending along the path, so that a side edge of each successive banknote under test moves along the path whilst abutting the guide rail. In this way, consistent data can be derived from banknote to banknote, that can be compared with the reference data for acceptable banknotes stored in the memory. In order to compare banknotes of different sizes, proposals have been made in the past to use a stepped entrance path with steps of different widths to align different width banknotes with the path through the detector array. However, this does not work well with crinkled or damaged banknotes. Also, mechanically driven guide plates have been proposed, that move transversely of the path in order to urge the banknotes of different widths against the guide rail or centrally of the path. These mechanical arrangements for aligning the banknote are mechanically complicated and so add significantly to the cost of the banknote acceptor. Also, they can be unreliable and not accurately guide the banknote along the desired path.
Proposals have been made to scan a banknote and to transform all the scanned data for counting purposes, as described in U.S. Pat. No. 5,680,472 but the process involves large amounts of data and is computationally slow.
The present invention seeks to overcome these problems and disadvantages.